Frictionally welded thermoplastic articles having improved strength

Abstract

A frictionally welded, filled thermoplastic article is strengthened by restricting lateral flow of molten material out of the gap between the workpieces, so that a molten pool of substantial depth is maintained from the beginning of melting to the onset of solidification. The restriction to lateral flow of material is provided by dams (projections) of essentially rectangular cross-section at each lateral edge of one of the workpieces, while the other workpiece has a substantially flat mating surface.

What is claimed is:  
     
       1. A method of frictional welding a first thermo-plastic workpiece to a second thermoplastic workpiece, comprising the steps of: 
       a. pressing the first and second workpieces together under a compressive clamping pressure;  
       b. moving the first workpiece relative to the second workpiece in a plane parallel to their interface sufficient to frictionally heat the interface;  
       c. melting the interfacial surfaces of the first and second workpieces creating a melt down region;  
       d. providing a means to restricting the lateral flow of molten material out of the gap between said interfacial surfaces; and  
       e. retaining a molten pool of substantial depth between the workpieces from the beginning of melting to the onset of solidification,  
       and wherein at least one of said first and second workpieces is comprised of a fiber reinforced thermoplastic; 
       wherein said restricting means is a substantially rectangular projection along each lateral edge of said first workpiece and the thickness of each of said projections is between about 5% and about 35% of the thickness of said first workpiece, and wherein the height of each of said projections, relative to the lowest point on the initial mating surface, is at least about 25% of the dimension of the melt down region. 
     
     
       2. A method as recited by  claim 1 , wherein said restricting means is a substantially rectangular projection along each lateral edge of said first workpiece, and said mating surface of said second workpiece is substantially flat. 
     
     
       3. A method as recited by  claim 1 , wherein, prior to welding, the cross-sectional area of the space defined by a line between the upper edges of the rectangular projections and the material surfaces between them is at least about 15% of the product of the thickness of the first workpiece and the dimensions of the melt down region. 
     
     
       4. A method as recited by  claim 1 , wherein the relative motion between the first and the second workpieces is a linear vibratory motion. 
     
     
       5. A method as recited by  claim 1 , wherein the relative motion between the first and second workpieces is an orbital motion. 
     
     
       6. A method as recited by  claim 1 , wherein the relative motion between the first and second workpieces is a rotational motion. 
     
     
       7. A method as recited by  claim 1 , wherein each of said thermoplastic workpieces comprises a thermoplastic polymer selected from the group consisting of polyamides, polyesters, polycarbonates, polysulfones, polyimides, polyurethanes, polyethers, polyolefins, vinyl polymers and mixtures thereof. 
     
     
       8. A method as recited by  claim 7 , wherein each of said thermoplastic workpieces comprises a polyamide.